The present invention relates to removing coke from a coker drum in a delayed coker unit. In particular, the present invention relates to coke cutting using high pressure water jets. Delayed cokers are operated in a semi-batch mode, with at least two drums. While one is being filled and coked, the other is de-coked. During the coking cycle, the drum is gradually filled with liquid feed at about 900 degree F. from a nozzle at the bottom of the drum, vapor product leaves the drum at the top, and coke forms inside the drum as the result of a complex solidification process. During de-coking cycle, the drum is first cooled by steam or water. After cooling and draining, a high pressure rotary jet is used to cut the coke loose, which is removed from the bottom of the drum. Since the high pressure water jet literally cuts through the layers of coke in the coker drum, the process of emptying the coke drum using the water jet is commonly called “coke cutting.”
Delayed cokers are recognized as one of the primary capacity bottlenecks at a refinery. Quenching, cutting and removal of the solid coke are the limiting steps of the coker operation. Currently there are very few measurements on a coker for operators to determine actual condition of de-coking operation and make real-time adjustment. The coke cutting and removal in most delayed cokers is a labor-intensive manual operation.
The cutting process relies heavily on the person operating the hydraulic decoking system. The coke cutting operator uses the rotary water jet to cut through the coke, starting from the top of the drum, removing one layer of coke each time, then moves the jet downward to cut the next layer. The operator determines when to move to next layer either by fixed-time routine or by listening to the air-born sound emitted from the top opening of the drum. Very often, more round trips of the water jet are performed over the layer just to increase the probability of complete removal of all the coke in that layer. When the operator could not determine the cutting condition from his own sensing capability (e.g., when moved from the vicinity of the drum opening to an isolated control room), it is not only very challenging to cut coke efficiently but also increases the probability of equipment failure such as bending damage of the jet bit due to coke fallouts from residual coke left behind (i.e. above the water jet cutting tool).
The operator is responsible for controlling or driving the rotary water jet down and up the coker drum until he thinks that all the coke inside the drum has been removed. The operator becomes the sole decision maker during the cutting operation and so the potential for error is very high. In addition, the cutting time and quality also vary from operator to operator and from cycle to cycle. To make the coke cutting operation more efficient, more consistent, and safer, there is need to monitor the coke cutting operation with sensors and a computerized intelligent system to assist operators in coke cutting.
The present invention uses acoustic approach to measure the drum wall vibration caused by the coke cutting, and convert the vibrational signature measurement into an intelligent decision-making system which is capable of classifying the different conditions of the cutting operation in real-time. This intelligent capability leads to partial or full automation of the coke cutting operation. The invention allows for very efficient coke cutting, largely eliminating the possibility of errors that arise from misjudgments of the coke cutting operator. The invention converts coke cutting from an arbitrary process lacking of controls into a very reliable and consistent operation. This translates into safer operation, lower operational costs and higher productivity.